1. Field of the Invention
The present invention relates to a process for producing a microlens array being able to condense light at a high efficiency, an electrolytic solution therefor, and an apparatus for producing a microlens array.
2. Description of Related Art
As a process for producing a microlens array, such methods have been used as a dry etching method, represented by a reactive ion etching method (RIE method), a lithography method using emitted light or an X-ray (LIGA method), a focused ion beam method (FIB method), a doping method of a high refractive index material by thermal diffusion, a method of melting a resist film by heating (resist flow method), and a method of casting a plastic material in a mold previously formed by the RIE method to form a microlens array (stamper method).
The RIE method, the LIGA method and the FIB method require an expensive apparatus and a prolonged etching time to cause high cost.
The doping method of a high refractive index material by thermal diffusion has an advantage of the use of a flat plate, but it suffers some limitations that the shape and the curvature of the lenses were restricted since they are controlled only by the refractive index, and it can be applied only to a heat resistant material, i.e., a glass substrate.
The resist flow method is preferred as a method of directly forming on a CCD, but it is limited in the shape of the lenses and is not suitable for a microlens for collimation.
The method of preparing a mold previously formed can reduce the production cost, but it has such a problem in that the formation of the mold requires the expensive RIE method.
In all the methods, it is the current situation that high production cost is required upon producing a microlens array having a large area and a high density, and there is no production method of microlenses that is simple and has high degree of freedom.
A method of implanting microbeads in a binder resin is known as a low cost method. Although it is advantageous in mass production and production in large areas, it has such a problem in that it is difficult that the microbeads are uniformly arranged.
The inventors have proposed a process for forming an image excellent in resolution and a process for producing a color filter, in which electrodeposition or photoelectrodeposition are carried out at a low voltage application by using an electrodeposition material containing a colored material. The processes are disclosed in detail in JP-A-10-119414, JP-A-11-189899, JP-A-11-105418, JP-A-11-174790, JP-A-11-133224 and JP-A-11-335894. The process for forming an image and the process for producing a color filter have such characteristic features that a colored film with high resolution can be formed in a convenient method, but they are the techniques that are mainly applied to the field of a display device, such as a liquid crystal display device.
The inventors have also proposed a photocatalytic film deposition method capable of forming a colored film, such as a color filter, with high resolution by the convenient method as similar to the foregoing methods (disclosed in JP-A-2001-140096).
On the other hand, a microlens array is used as an optical element, such as a condenser lens, as well as a display device, such as a liquid crystal projector. Furthermore, as described in the foregoing, it is the current situation that a microlens array is produced by micro fabrication through complicated process steps including a photolithography method of a photosensitive material, and there is no attempt to produce a microlens array by an electrodeposition method using no complicated process, such as the RIE method.
The invention has been made in view of the foregoing problems associated with the conventional art and is to provide a process for producing a microlens array that can produce a microlens array with low cost in a convenient method and can freely adjust the density of the microlenses, and an electrolytic solution and a production apparatus therefor.
The invention relates to, as one aspect, a process for producing a microlens array containing the steps of: arranging a master substrate having an insulating substrate, an electroconductive thin film and a photosemiconductor thin film in this order, preparing an aqueous electrolytic solution containing a film forming material having a solubility of dispersibility in an aqueous liquid decreasing upon changing pH; forming a microlens array master by contacting the semiconductor with the aqueous electrolytic solution and irradiating the photosemiconductor thin film with a light so as to induce the pH change of the electrolytic solution enough to selectively deposit the film forming material on the master substrate; forming a layer of a template resin material on a surface of the master and releasing the layer therefrom to produce a template; and forming a layer of a microlens array resin material having a controlled refractive index on the template and releasing the template therefrom to produce a microlens array.
The invention also relates to, as another aspect, a process for producing a microlens array containing the steps of: arranging a master substrate having an insulating substrate, an electroconductive thin film and a photosemiconductor thin film in this order, preparing an aqueous electrolytic solution containing a film forming material having a solubility or dispersibility in an aqueous liquid decreasing upon changing pH; forming a microlens array master by contacting the photosemiconductor thin film and the electroconductive thin film with the aqueous electrolytic solution and irradiating the photosemiconductor thin film with a light so as to induce the pH change of the electrolytic solution enough to selectively deposit the film forming material on the master substrate; forming a layer of a template resin material on a surface of the master and releasing the layer therefrom to produce a template; and forming a layer of a microlens array resin material having a controlled refractive index on the template and releasing the template therefrom to produce a microlens array.